I've been to Luanda a couple of times and it is really a city of contrasts. There is a LOT of oil money (and diamonds too) but almost none of it gets to the population. The roads in Luanda... well... It used to take me upwards of 45 minutes to drive within the city to get to work. I can concur that life IS expensive. Things like restaurants ARE exorbitant, but beer is cheap like water. All that being said; I actually like the place.
with respect to crime; I did not get the impression that it was better/worse than anywhere else.